1. Field of the Invention
This invention relates generally to variable resistors and potentiometers and more particularly to the fabrication of contact wipers and the assembly thereof into rotor blanks of these variable resistors and potentiometers.
2. Description of the Prior Art
Variable resistors or potentiometers are known in the prior art in which the parts are held together by rivets and/or bolts. In some of these earlier devices the heat, necessarily generated by welding, destroyed the temper of the wiper spring material thus rendering it useless and the potentiometers thus manufactured inoperative. In many cases, undesirable noise resulted from the imperfect engagement between the sliding wiper contact and the resistance element. Elimination of these problems made the potentiometer design complicated and accordingly prohibitively expensive. Some of the wiping brushes of the prior art were formed by hand, as is related in U.S. Pat. No. 2,760,036 to R. C. Raymer at column 8, starting at line 58. In this fabrication a dull razor blade was actually employed to "press the short end of the blank into the groove 136, thereby forming a V-shaped contact portion 138". Obviously, if the razor blade were not dull enough, so that the material was cut through, the operation would have to be repeated with a suitably blunt razor blade. In this prior art assembly, it was also necessary to employ a "suitable conducting cement" and "a heat resisting paint or laquer". In further complication, it was necessary to use very expensive contact materials as the inventor reports at column 13, starting at line 42: "In practice, the brush is composed of a soft noble metal or a noble metal alloy. Among the metals found suitable for use in the wiper brush are platinum, paladium, nickel, gold and soft alloys thereof." It is of interest to note that a total of more than 40 tedious steps are required in the fabrication of the wiper brush and its assembly into the rotor blank in the described device. In U.S. Pat. No. 3,010,090 to Vacha, there are mentioned at least some of the effects of soldering in the assembly of these instruments. He finds that too much solder increases the mass at the end of the contact thus resulting in variations in contact resistance under certain vibratory conditions and, by contrast, too little solder leads to joint failure due to fatique. Herein it is also noted that "the application of heat to weld or solder the parts affects the temper of the spring adversely."
As is made increasingly evident by an examination of the prior art, it has been necessary to perform a large number of operations, some of which must be performed by hand, with the attendant rejection of many parts, thus, exorbitant assembly expense has been involved. It is also made evident by such examination that the potentiometer manufacturing art suffered from much uncertainty and much waste through the fabrication of many unusable units and a great number of faulty parts.
Attention is invited to the following listed prior art patents for an indication of the order of difficulty encountered in the manufacture of these instruments in the immediate past.
______________________________________ U.S. Pat. No. Title Inventor ______________________________________ 1,399,492 Double Switch Blade H. Krantz 2,291,246 Volume Control J. Marsten 2,760,036 Metallic Film Potentiometer R. C. Raymer 2,956,253 Potentiometer J. Clayton, Jr. et al 3,010,090 Slider Contact F. P. Vacha 3,119,088 Wiper Assembly for a M. J. Fliegler Multiturn Potentiometer et al 3,274,368 Laminated Distributor Brush J. L. DeBoo et al 3,328,707 Wiper Assembly for Potentio- A. S. Louis et al meters 3,704,436 Multiware Potentiometer R. L. Froebe et al Contact Device ______________________________________
A novelty search conducted in the U.S. Patent and Trademark Office for the purpose of locating any patents relevant to the subject matter of the present invention resulted in the discovery of U.S. Pat. No. 3,733,695, Method of Making Potentiometer Terminations, by S. W. Frey, Jr. et al. The field of this search included:
Class 29--Metal Working PA0 Subclasses 621 and 630
It would, therefore, as indicated by research into the subject, be a great advantage to the art to provide an improved wiper contact spring and method of assembly.
It would be a further advantage to provide such an improved wiper contact spring at a greatly reduced unit cost.
Another advantage would be the reduction of the number and complexity of the steps required presently in the fabrication of a potentiometer contact and rotor.
An additional advantage would be the provision of a combination of the manufacture of multiwire contact springs with the assembly of the contact spring into a rotor so that both manufacture and assembly become one integrated process.
It would, of course, be a desirable advantage to provide the above advantages in an economical process.